This invention relates to a power converter assembly.
A typical DC-to-DC power converter assembly, for example, includes power-dissipating semiconductor components, such as transistors, SCRs, and rectifiers, magnetic energy storage elements, such as transformers and output filter inductors that have magnetic cores surrounded by one or more windings and electric energy storage elements, such as input and output filter capacitors.
A DC-DC power converter is often packaged in a rectangular xe2x80x9cbrickxe2x80x9d format, as shown in FIG. 1. Heat dissipated by components within the converter 100 is withdrawn through a metal surface 102, referred to as a baseplate. Electrical connections to the converter are made through pins 104.
In one known kind of power converter assembly, as shown in FIG. 2, the baseplate 103 includes a metal plate 102 bonded to an insulating layer 106. Components on the top surface 108 of the insulating layer 106, such as transformer 110 and resistor 112, are interconnected by conductive traces 113 on surface 108. Power dissipating components (e.g., a power semiconductor 114) are mounted directly on the top surface of the insulating medium so that dissipated heat is removed through the baseplate. A printed circuit board assembly 116, which also has conductive traces 117 that interconnect control electronics and other components (e.g., an integrated circuit 118), is mounted above the baseplate 103 on standoffs 119. Electrical connections between the printed circuit board assembly 116 and components and traces on the top surface of the baseplate 103 are made through pins 120 and component leads (e.g., a lead 122 of power semiconductor 114). (As used herein the terms xe2x80x9ccomponentxe2x80x9d and xe2x80x9ccircuit elementxe2x80x9d refer to electronic or energy storage components (e.g., semiconductors, resistors, capacitors and magnetic devices) and excludes interconnection devices (e.g, termination pins, connectors) and packaging and assembly elements (e.g., standoffs, cases).)
Another known kind of power converter assembly, shown in FIG. 3A, also has a baseplate assembly 124 and a printed circuit board assembly 126. Power dissipating devices 128 are mounted on the baseplate assembly. The printed circuit board assembly includes components, such as a transformer 130 and an output inductor 132, mounted on a printed circuit board 127. A non-conductive case 129 attaches to the baseplate 124, enclosing the printed circuit board assembly 126. The power converter assembly 100 is filled with an encapsulating material (not shown).
As shown in FIG. 3B, and described in U.S. Pat. No. 5,722,508, xe2x80x9cPackaging Electrical Circuitsxe2x80x9d (assigned to the same assignee as this application and incorporated by reference), the baseplate assembly 124 may include a metal heat-spreading plate 142 separated from the metal plate 102 by an insulating sheet 144. Power dissipating components 128 include a semiconductor die 134 mounted on and connected to conductive pads 136 on the surface of an insulating substrate 138. The substrate 138 is connected to the heat spreading plate 142 by solder 140. Conductive traces 146 on the printed circuit board 127 connect to conductive pads 136 on the power-dissipating device 128 through solder 148.
In a third known kind of power converter assembly, shown in FIGS. 4A and 4B, a printed circuit board assembly 150 includes components 160a, 160b mounted on both sides of a printed circuit board 152. A xe2x80x9cprinted circuit transformerxe2x80x9d on the circuit board assembly includes a magnetic core 154, which passes through holes 156a, 156b in the printed circuit board. Windings (not shown), formed by conductive etches on the surfaces of one or more layers of the printed circuit board, surround the holes 156a, 156b and the core. The distances by which the core 154 extends above and below the printed circuit board 152 are approximately equal. Power dissipating semiconductors 158, and other components of various heights 160b, are mounted on the side of the printed circuit board which faces an inside surface 162 of a metal case 164. An encapsulant 166 fills the space between the printed circuit board assembly 150 and the metal case. Heat from the power dissipating components 158 passes through the encapsulant 166 and into the metal case 164.
In general, in one aspect the invention features a power converter assembly comprising a heat sinking plate, a circuit board structure having a side that faces and is spaced by a gap from a surface of the heat sinking plate that is nearer to said side, a dissipative semiconductor component mounted on said side, and an encapsulating material filling the gap, the gap being characterized by an average thermal-resistance of less than 3xc2x0 C.xe2x88x92in2/Watt.
Implementations of the invention may include one or more of the following features. The heat sinking plate may be planar. The circuit board structure may include a planar circuit board that holds power conversion elements of a power converter circuit. The power conversion elements may include a transformer having cores and in which no portion of any of the cores lies in the gap. The power conversion elements include the semiconductor component. The semiconductor component may include a MOSFET or a diode. The average thermal resistance may be less than 2xc2x0 C.xe2x88x92in2/Watt. The average thermal resistance may be less than 1xc2x0 C.xe2x88x92in2/Watt.
In general, in another aspect of the invention, components on the circuit board structure together comprise a power conversion circuit that is capable of accepting power from a source and delivering power to a load, the components including a semiconductor component mounted on the side of the circuit board that faces the surface of the heat sinking plate. The circuit board divides the total volume occupied by the assembly into a gap volume between the circuit board and the plate, and a remaining volume, the gap volume being no more than 25% of the total volume.
Implementations of the invention may include one or more of the following features. The power conversion elements may include a transformer having cores and in which no portion of any of the cores lies in the gap. The gap volume may be no more than 15% of the total volume, preferably no more than 10% of the total volume.
In general, in another aspect of the invention, the gap has a gap volume that is enclosed by (a) the surface of the heat sinking plate, (b) the side of the circuit board that faces the surface of the heat sinking plate, and (c) a perimeter surface that connects the perimeters of (a) and (b) and which extends perpendicular to, and upward from, the surface of said heat sinking plate. The upper volume is enclosed by (a) the surface of the heat sinking plate, (b) an imaginary plane that is parallel to and spaced above the side of the circuit board which does not face the surface of the heat sinking plate, the plane being tangent to the top of a component without intersecting any other component, and (c) the perimeter surface. The gap volume is no more than 25% of the upper volume.
In general, in another aspect of the invention, no part of the permeable core of a magnetic power conversion component faces the side of the circuit board that faces the surface of the heat sinking plate.
Among the advantages of the invention are that internal temperature rises of components within a power converter may be kept small while the circuit board and baseplate of a power converter can be fabricated less expensively, more easily, and with higher yield than when heat-dissipating devices are mounted directly on the baseplate before the baseplate is attached to the circuit board assembly. A larger number of small power dissipating semiconductor devices can be used because the assembly technique is relatively forgiving and yield losses are still within acceptable levels. This permits placing the switching devices in locations on the board that are closer to the portions of the circuit to which they connect while spreading out the heat to enable the encapsulant to transfer it to the baseplate with a low temperature rise.
Other advantages and features will become apparent from the following description and from the claims.